Two distinctive stages of novelty processing revealed by high-density EEG based source imaging

Novelty detection is an evolutionarily significant and ancient function as well as a relatively stable function whose early life status marks for long-term developmental outcomes and predicts a range of adult functions. While various brain regions have been shown to respond to environmental novelty, how different brain regions coordinate in novelty related information processing remains under-explored. Here using a combination of high-density EEG, second order blind identification (SOBI), and a standard visual oddball task, we test, in humans, a two-stage novelty processing hypothesis which states that two distinct stages of novelty processing exist, one involves early-occurring domain-specific neural activity in the sensory processing areas of the brain and the other involves later-occurring domain-general neural activity involving brain regions beyond the sensory cortices. We found that: (1) a significant Novelty effect (oddball effects) not only in the SOBI-recovered Late component (P300 component) but also in the Early component (N150 visual) offering first EEG evidence for oddball effect in the sensory domain; (2) a significant Stage (Early vs Late) by Frequency (delta, theta, alpha, beta, and gamma) interaction effect indicating two functionally dissociable mechanisms underlying novelty detection; (3) a significantly shorter latency in odd-ball related theta power increase in the Early visual than in the late P300 component. These results not only offer support for the two-stage novelty processing theory but also provide new evidence for an early involvement of theta power increase in the novelty processing.

Novelty Processing Depends on Medial Temporal Lobe Structures

ObjectivesThe goal of the present study was to identify the role of the medial temporal lobe (MTL) in the detection and later processing of novelty stimuli.MethodsTwenty-one epilepsy patients with unilateral MTL resection (10 left-sided; 11 right-sided) performed an adapted visual novelty oddball task. In this task two streams of stimuli were presented on the left and right of fixation while the patients’ electroencephalogram was measured. Patients responded to infrequent target stimuli, while ignoring frequent standard, and infrequent novel stimuli that could appear either contra- or ipsilateral to the resected side.ResultsNovelty detection, as indexed by the N2 ERP component elicited by novels, was not affected by the MTL resections. Later processing of novels, however, as indexed by the novelty P3 ERP component, was reduced for novels presented contra-versus ipsilateral to the resected side. Target processing, as indexed by the P3b, was unaffected.ConclusionsThe current results suggest that MTL structures play a role in novelty processing, but that the novelty signal may originate from a distinct neural source.